Method of decolorizing water

ABSTRACT

A method of decolorising water colored by humic or fulvic acid, such as moorland runoff water, which method comprises bringing the water into contact with chitin or alginic acid as adsorbent. The adsorbent may be recycled after use by treatment with aqueous alkaline solution followed by treatment with an aqueous acid solution.

This invention relates to a method of decolourising water comprisinghumic or fulvic acid, for example moorland runoff water.

Water, such as that which runs off moorland, is coloured and as a resultis aesthetically undesirable and unacceptable to customers. In additionhumic substances may react with halogens, e.g. chlorine, during watertreatment to produce trihalomethanes or other organohalogens(organhalons) which may represent a health hazard. Humic substances alsoreduce the effectiveness of chlorine disinfection. Colouration of watercan be particularly pronounced following heavy rain after a drought. Itis known that the colour may be removed from such water by chemicalprecipitation methods using for example aluminium sulphate and hydratedlime to adjust pH, followed by mixing, flocculation and physicalseparation of the flocs by for example air flotation. It is also knownthat activated carbon may be used to remove colour from water but thisis expensive to regenerate and relatively inefficient and so activatedcarbon is generally only use for removal of odour/taste andpharmaceuticals such as unmetabolised drugs or their breakdown products.A further way to remove colour from water involves the use ofion-exchange resins. However, this is relatively expensive since theresins are expensive to regenerate.

It has now been found that colour may be effectively removed from suchcoloured water by adsorption of colouring components onto chitin oralginic acid. Chitin and alginic acid are low cost biomass materialswhich are readily available in large quantities.

The present invention therefore provides a method of decolourising watercoloured by humic or fulvic acid, which method comprises bringing thewater into contact with chitin or alginic acid as adsorbent. Theinvention also provides the use of chitin or alginic acid to decolourisesuch water. In this way the level of colour in the water can be reducedto an acceptable level.

An acceptable level of colour in the water may, for example, be a levelof less than 20 Mazen units. Alternatively an acceptable level of colourmay be such that the water may be mixed with uncoloured water to providewater with a colour level of less than 20 Hazen units. For example waterwith a colour level of less than 40 Hazen units may be mixed with equalvolumes of uncoloured water to provide water with a colour level of lessthan 20 Haze units.

The colour of water is expressed in terms of Hazen units and one Hazenunit is defined as the colour produced by 1 mg/l of platinum in the formof chloroplatinic acid in the presence of 2 mg/l of cobaltous chloridehexahydrate. Samples are compared against standards either visually, orphotoelectrically using a previously constructed calibration graph.

The water to be decolourised by the method of the present inventioncomprises humic and/or fulvic acid. These are polyphenolic acids foundin the "humic fraction" of soils. The acids are formed as products ofthe anaerobic digestion of lignin and are resistant to furtherbreakdown. They are formed as breakdown products of peat and producecolouration in for instance moorland runoff waters, e.g. acidic orneutral moorland runoff waters.

The coloured water may also contain additional contaminants such asother polyphenolic acids including those found in industrial waste andsuch as particulate material as turbidity and metal ions, e.g.aluminium, manganese or iron. Such additional contaminants may also beadsorbed by the adsorbent. Alternatively the coloured water may besubstantially free of other contaminants such as metal ions.

The coloured water used in the method of the present invention istypically naturally neutral or acidic and has a pH from 5 to 7. The pHmay however be specifically adjusted to optimise a particular step inwater treatment such as flocculation, or aluminium or iron saltprecipitation and may be outside this range.

The adsorbent used in the method of the present invention adsorbscoloured compounds, such as humic or fulvic acid, present in the waterand so decolourises the water. The adsorbent may be chitin or alginicacid, and is preferably chitin. Chitin is a polysaccharide made up ofmolecules of N-acetylglucosamine linked together by 1,4-β glycosidicbonds. It occurs in the exoskeleton of shellfish and insects, and may bereadily obtained as a by-product of shellfish industries. Thus, a sourceof chitin is from the exoskeleton of shrimps or crabs. Crab-derivedchitin is preferred. Chitin is also found in the cell walls of fungisuch as basidiomycetes, ascomycetes and zygomycetes. Alginic acid is alinear polysaccharide polymer made up of β-(1,4)-D-mannosyluronic acidand - (1.4)-L-gulosyluronic acid residues which occurs in seaweed and isreadily obtained therefrom.

The adsorbent may be pre-treated prior to use, for example to removecontaminants or to enhance colour removal performance. A suitablepretreatment involves heating the chitin in an alkali solution, egsodium hydroxide. Suitably, a solution of 0.05 to 0.3 M sodium hydroxidemay be used. The chitin may be heated in the alkali solution at atemperature of for example, about 70 C. Typically, 31 of alkali solutionfor 500g of chitin may be used. After heating for a suitable period oftime, eg about 2 hours, the chitin is rinsed with water. When chitin hasbeen pretreated in this manner, it is desirable that the chitin is thenwashed (prewashed) further in acid in order to enhance its colourremoval properties. Acid at a concentration of from 0.01 to 1 M may beused. Preferably, hydrochloric acid is used for this prewash. Typically,HCl at a concentration of 0.01 to 0.1 M eg. 0.01 to 0.05 M, is required.The prewash may be performed at room temperature.

The adsorbent may be used in any conventional form, such as for exampleas particles, beads, sheets or fibres. In particular particles may beused which are typically 0.5-10 mm in diameter, preferably from 0.5 to 2mm in diameter.

The water may be contacted with the adsorbent by any conventionalmethod. The treatment may for instance be performed as a mixed batchprocess in which adsorbent is mixed with a batch of coloured water andis then removed for example by filtration, sedimentation orcentrifugation and decantation of a supernatant.

Preferably however the water is contacted with a bed, such as a packedbed, of adsorbent for instance in the form of a packed column ofadsorbent. Other types of bed include a fluidised bed, a tricklingfilter bed or a slow filter bed. The type of arrangement which may beused can be selected by a person of skill in the art and will depend onfactors such as the quantity of water to be treated and the condition ofthe water prior to treatment. The factors can be assessed by those ofskill in the art familiar with water filtration systems in the light ofthe present invention. Water decolourisation may then be carried out ina continuous manner by passing coloured water through or over a bed. Forexample a packed bed comprises packed adsorbent through which the waterto be treated is pumped or percolated under gravity to effect contactbetween the water and the adsorbent.

In a situation where the turbidity of the water to be decolourised ishigh, it is desirable to prefilter the water prior to contact withchitin. In the case of a continuous filtering process, this may beachieved by insertion of a prefilter in line ahead of a bed in order totrap particulate material and prevent blinding of the bed. Such aprefilter may consist of coarse chitin (e.g. of a particle size of 1 to10 mm) or coarse sand (e.g. mesh 16/30), and will generally be shorterthan the bed. It will be backflushed regularly with water to removeparticulate material.

In a batch treatment the amount of adsorbent is preferably from 0.01 to1.0, especially about 0.1, g of dry adsorbent per 10 ml of water. In acontinuous treatment preferably 25 to 2500, more preferably 25 to 250,volumes of water per volume of adsorbent, are treated by contact with apacked bed, without recycling of adsorbent.

After the decolourising treatment, the water may be further treated torender it suitable for use as drinking water, for example bychlorination. The water may also be further treated if it is notintended for use as drinking water, to render it suitable for industrialor agricultural use. Such treatment may for example include aerobic oranaerobic microbial treatment, activated carbon treatment, sandfiltration, flocculation, ultrafiltration or reverse osmosis. Thesetreatments may also take place prior to treatment with chitin.

Following treatment of the water with adsorbent the adsorbent may beregenerated and recycled by treatment with an aqueous alkaline solution,comprising e.g. NaOH, to release the adsorbed coloured compounds andother adsorped materials (eg metal ions) from the adsorbent. Theadsorbent may be treated as a batch following removal of adsorbent froma batch treatment or following removal of adsorbent from a packed bedfollowing a continuous treatment. Alternatively, in the case of acontinuous decolourising treatment the adsorbent may be recycled bypassing aqueous alkaline solution through the bed of adsorbent.

After treatment with alkali the adsorbent may be reactivated bycontacting with acidic water prior to reuse of the adsorbent in thetreatment of coloured water. This treatment may take the form of aprewash of the type described above for the preparation of freshadsorbent.

The concentration of the alkaline solution may for example be from 0.001to 5.0M, such as from 0.01M to 0.5M and preferably 0.025 to 0.5M, in thecase of NaOH or may be an equivalent concentration of another alkali, egpotassium hydroxide.

The amount of alkaline solution used to recycle the adsorbent in a batchrecycling treatment is typically from 0.2 to 2 ml of 0.05M NaOH per g ofadsorbent. The amount of alkali or acid required to regenerate andrecycle adsorbent by passing through a packed bed is typically from 1 to4 bed volumes, for example about 2 bed volumes followed by 2 bed volumesof acid. For example 2 bed volumes of 0.05M NaOH followed by 2 bedvolumes of 0.05M HCl may be used. The recycling process is preferablyselected so that colour is eluted in one bed volume or less. Regenerantsolutions of acid and alkali may be discarded to waste but arepreferably recharged to reach original strength and reused to minimisewaste volumes.

The invention will now be illustrated by reference to the followingExamples:

EXAMPLES Growth and Preparation of Microorganisms For Colour RemovalExperiments.

Bacteria were grown in Oxoid Nutrient Broth CM1 in 2 l flasks containing1 l of medium. The cultures were inoculated to start growth with a 1%v/v inoculum of a 1 day old starter culture and incubated at 30° C. for48 hours on a rotational shaker at 200 rpm to allow the cultures toreach stationary phase. The bacteria were harvested by centrifugation at50,000 x g for 10 minutes followed by 3 washes in distilled water at50,000 x g for I0 minutes before resuspension to a known volume.

Fungi were grown in Aspergillus Complete Medium in 2 l flasks containing1 l medium. Growth was initiated by adding 1 ml of a spore suspensionprepared by vigorously shaking a 10 mm diameter plug of a sporulatedpotato dextrose agar petri dish culture with 10 ml of water. Cultureswere incubated for 5 days at 20° C. on a rotational shaker at 200 rpm toallow the cultures to reach stationary phase. Fungal mycelium washarvested by filtration through Whatman No. 91 filter paper followed bywashing 3 times with distilled water.

Production of Lignin

Wheat straw was treated with dilute sulphuric acid (2% w/v) for 12 hoursat 90° C. This hydrolysed the straw hemicellulose content. The remainingmaterial was washed thoroughly with distilled water and dried at 100° C.to produce a crude lignin preparation. The yield of lignin from thestraw was 60.0% on a dry weight basis.

Other materials were obtained from commercial sources. Brewers yeast hadbeen freeze-dried for storage

Known volumes of bacterial suspension were placed in a pre-weighed glassbeaker and dried to constant weight at 100° C. oven. Known wet weightsof fungal biomass were dried to constant weight. Biomass materials thatwere available in a dry form (chitin, chitosan, lignin, alginic acid,yeast) were weighed out directly for contact and other experiments.

Water samples were filtered through Whatman No. 91 filter paper toremove large particulate matter prior to use.

EXAMPLES 1 AND 2

30 ml of moorland runoff water coloured by humic and fulvic acids at anunaltered pH of 5.4 were mixed with a known weight (about 0.3 g) ofpre-dried chitin (Example 1) or alginic acid (Example 2). The mixturewas left standing at room temperature (about 22° C.) for 15 minutes thenseparated by filtration through Whatman No. 1 filter paper.

Colour was measured by absorbence at 400 nm against a distilled waterblank. Glass cuvettes of path length 40 mm were routinely used.Measurements at individual wavelengths and wavelength scans wereperformed using a Pye-Unicam SP400 uv/visible Spectrophotometer.Readings given in the results correspond to apparent colour as thesamples were not routinely passed through 0.45 μm filters which wouldgive the true colour reading. The results are shown in Table 1 below.

COMPARATIVE EXAMPLE 1-11

Examples 1 and 2 were repeated using a variety of different materials asshown in Table 1. In the case of fungal mycelium a known weight (about0.5 g) was used and in the case of bacterial suspensions a known volume(about 0.3 ml) was used. In the case of bacterial suspensions thebacteria were removed by centrifugation at 50,000 x g for 10 minutesfollowed by decanting of the supernatant rather than by filtration. Theresults are shown in Table 1 below.

                  TABLE 1                                                         ______________________________________                                        Percentage Reduction in Absorbency at 400 nm                                                   Percentage Reduction                                                          in Absorbency at 400 nm                                      Example   Biomass      Mean      s.d.   n                                     ______________________________________                                        1         Chitin       21        0.92   5                                     Comp 1    Chitosan      2        0.05   5                                     Comp 2    Lignin       nr               1                                     2         Alginic Acid 25        0.53   5                                     Comp 3    Peat         nr               1                                     Comp 4    Bacillus     14               1                                     Comp 5    Pseudomonas  nr               1                                     Comp 6    Bacillus      8               1                                     Comp 7    Citrobacter  nr               1                                     Comp 8    Mucor sp.    nr               1                                     Comp 9    Penicillium sp.                                                                            nr               1                                     Comp 10   Aspergillus sp.                                                                            nr               1                                     Comp 11   Yeast        nr               1                                     ______________________________________                                         nr -- no removal                                                              n -- number of determinations                                                 sd -- standard deviation                                                 

It can be seen that chitin and alginic acid are the most effectivematerials for removing colour under the conditions of this experiment.Some colour removal was seen with chitosan and bacterial biomass fromtwo Bacillus species, however the quantity of removal was not suitablefor continuing experimentation. Chitin and alginic acid were thereforestudied in packed bed systems.

EXAMPLE 3 Alginic Acid Packed Bed

Pre-swollen alginic acid (approximately 14 g on a dry weight basis) waspacked into a 30 cm×1.5 cm diameter column (column volume 53 ml).Moorland runoff water coloured by humic and fulvic acids (adjusted to pHof 7.0 by addition of saturated Ca(OH)₂) was passed through the columnat a rate of 60 ml per hour. Fractions of approximately 15 ml werecollected at 15 minute intervals. Approximately 3.3 l was passed throughthe column and once steady state had been reached between 25 and 30percent of material that absorbed at 400 nm was removed as measured bythe method described in Examples 1 and 2.

Control experiments indicated that acidification of the water to pH 3.6such as occurred on passage through this column of alginic acid reducedthe absorbence of the coloured water by about 7 percent.

EXAMPLE 4 Chitin Packed Bed

Chitin (5 g dry weight) was packed into a 20 cm×1.5 cm diameter column(column volume 35 ml). Moorland runoff water coloured by humic andfulvic acids was passed through the column at a rate of 13 ml per h andfractions collected at 60 min intervals. Approximately 910 ml was passedthrough the column with an average steady state removal of 74% ofmaterial that absorbed at 400 nm as measured by the method described inExamples 1 and 2.

The water eluted from this column was pooled and analysed, together witha sample of the water which was passed into the column.

                  TABLE 2                                                         ______________________________________                                        Analysis of Water Before and After Treatment                                  with Chitin                                                                   DETER-        RESULTS                                                         MINED    UNITS    Untreated Treated                                                                              % REMOVAL                                  ______________________________________                                        pH                6.0       6.0                                               Conductivity                                                                           uS/cm    276       360                                               Turbidity                                                                              ftu      3.4       1.8    47                                         True Colour                                                                            Hazen    70.8      10.2   86                                         Aluminium                                                                              mg/l Al  0.12      <0.04  >67                                        Manganese                                                                              mg/l Mn  0.05      0.03   40                                         Iron     mg/l Fe  0.62      0.11   82                                         ______________________________________                                    

The true colour reading in Hazen units due to dissolved matter wasmeasured on a sample passed through a 0.45 μm filter using thephotoelectric method of Knight, A.G. J. of Institution of WaterEngineers, 1951, 5, 623. Turbidity (as formazin turbidity units) wasdetermined by the standard HMSO method ("Colour and Turbidity of Waters.Methods for the Exdamination of Waters and Associated Materials 1981",HMSO Publications).

This analysis clearly shows the effectiveness of chitin at colourremoval. Chitin also shows significant metal binding properties andturbidity removal

EXAMPLE 5 Elution of Coloured Material from Chitin

The elution of coloured material from packed beds of chitin wasinvestigated. Samples of chitin (approx. 50 mg dry weight) taken from apacked bed containing 0.3 g of chitin through which 1910 ml of colouredwater had been passed were placed in 4 ml of 0.05M NaOH. The NaOHsolution was extremely effective at removing coloured material. A lowerconcentration of NaOH of 0.01M was also used. The extent of release wasthe same as that with 0.05 M NaOH although release took slightly longer.

COMPARATIVE EXAMPLE 12

Example 5 was repeated using 4 ml of 0.5M HCl in place of NaOH, but norelease of colour was observed.

COMPARATIVE EXAMPLE 13

Example 5 was repeated using 4 ml of 1M NaCl in place of NaOH. Somerelease of colour, though less than with NaOH, was observed.

EXAMPLE 6 Elution of Coloured Material from a Packed Bed of Chitin

A packed bed of 0.3 g of chitin through which 1460 ml of coloured waterhad been passed was eluted using 0.05 M NaOH. The bed volume of thechitin was about 1.5 ml and the coloured material was eluted within avolume of 8 ml NaOH solution.

EXAMPLE 7 Comparison of Colour Removal Performance by Ground (0.5-1.0mm) Shrimp and Crab Chitins in Packed Beds.

Single 30 cm columns were packed with either 5 g of ground shrimp chitinor 12 g of ground crab chitin giving bed lengths of 30 cm and total bedvolumes of 0.053 1 for both columns. Due to the higher packing densityof crab chitin, more than twice as much of this material could be packedinto a single bed than shrimp chitin.

The beds were washed with fresh tap water and 250 ml 0.01M HCl, then2.625 1 (49.5 bed volumes) of coloured water (initial true colour 31Hazen units) was pumped through both columns simultaneously (flow rate4.5 m/h).

Up to 99% removal of true colour was achieved by the crab chitin duringtreatment of the first 17 bed volumes of coloured water; the maximumremoval of colour obtained using the shrimp chitin was 85% and thisdropped below 80% after the passage of 7 bed volumes. After 30 bedvolumes of coloured water had been treated, the crab chitin was stillremoving 83% true colour with the shrimp chitin removing 39%. The higherpacking density of the crab chitin, allowing a much greater quantity ofchitin to be used in a single bed, is likely to be responsible for theenhanced colour removal performance of crab chitin.

EXAMPLE 8 Effect of Particle Size and Strength of Acid Pretreatment onColour Removal Performance of Crab Chitin

Packed beds of 30 cm in length were washed with 300 ml tap water and150-250 ml 0.01 or 0.05M HCl. The results of an investigation of theeffects of particle size and strength of acid pretreatment are shown inTable 3. Approximately 2.85l (57 bed volumes) of coloured water (initialtrue colour 30 Hazen units) were pumped through a 0.5-1.0 mm particlesize bed at 4.4 m/h pretreated with 0.01M HCl. Essentially complete(97-100%) removal of true colour was obtained for 30 bed volumes.Coloured water (initial true colour 36 Hazen units) was pumped throughanother 0.5-1 mm particle size bed pretreated with 0.05M HCl at 4.6m/h.Complete (100%) true colour removal was achieved for 39 bed volumes.Approximately 2.22 l (42 bed volumes) of moorland water (initial truecolour 36 Hazen units) were pumped through a 0.25-0.5 mm particle sizebed at 4.4 m/h pretreated with 0.01M HCl. Complete (100%) removal oftrue colour was achieved for 36 bed volumes.

Coloured material was eluted from the 0.25-0.5 mm bed using 4 bedvolumes of 0.025M NaOH. The chitin was then reacidified using 4 bedvolumes of 0.05M HCl. Coloured water (initial true colour 36 Hazenunits) was again pumped through the column at 4.4 m/h for 3.12 l (59 bedvolumes). Complete (100%) removal of true colour was achieved for 56 bedvolumes.

Thus decreasing the particle size relative to the bed diameter increasedthe quantity of crab chitin which could be packed into a single columnfrom 12 g to 14 g and also increased the colour removal performance Inaddition increasing the strength of the acid prewash from 0.01M to 0.05Msignificantly improved colour removal performance

                                      TABLE 3                                     __________________________________________________________________________    Effect of Pretreatments of Colour Removal                                     Performance by Crab Chitin                                                    Particle Size                                                                        Weight of                                                                           Bed Length                                                                          Strength HCl                                                                           Number of Bed Volumes Treated                     (mm)   Chitin (g)                                                                          (cm)  Pretreatment (M)                                                                       at 100% Colour Removal                            __________________________________________________________________________    0.5-1  12    30    0.01     30                                                0.5-1  12    30    0.05     39                                                 0.25-0.5                                                                            14    30    0.01     36                                                 0.25-0.5                                                                            14    30    0.05     56                                                __________________________________________________________________________

EXAMPLE 9 Regeneration of Chitin in Packed Beds Effect of AlkaliConcentration on Elution of Colour From Preloaded, Dried Chitin inMiniature Packed Beds.

Twelve 5 ml packed beds were packed with shrimp chitin which had beenpreviously loaded with colour and then dried. Colour was eluted from thecolumns using 0.05 M, 0.1M or 0.5M solutions of NaOH, KOH and Na₂ CO₃and distilled water as a control. Fractions of effluents were collectedand the apparent colour monitored by absorbance at 400 nm in 1 cm pathlength cells.

In all cases the amount of colour eluted increased with increasingconcentration of alkali (Table 4). NaOH and KOH eluted roughly equalamounts of colour at similar concentrations, both reagents were moreeffective at eluting colour than Na₂ CO₃. Insignificant amounts ofcolour were eluted using water.

                  TABLE 4                                                         ______________________________________                                        Comparison of the Performance of three different                              Chemical agents at eluting colour from Shrimp Chitin                                                    Absorbance at                                                                 400 nm of first                                                   Concentration                                                                             0.4 bed volume                                      Elution Agent (M)         eluted                                              ______________________________________                                        NaOH          0.5         2.33                                                              0.1         1.70                                                              0.05        1.51                                                KOH           0.5         2.32                                                              0.1         1.86                                                              0.05        1.39                                                Na.sub.2 CO.sub.3                                                                           0.5         1.29                                                              0.1         1.15                                                              0.05        1.18                                                Distilled Water                                                                             --          0.15                                                ______________________________________                                    

EXAMPLE 10 Effect of NaOH and HCl Regenerant Concentrations on ColourRemoval from Moorland Water by Crab Chitin

Four 0.3 m columns packed with crab chitin were prewashed with waterthen acidified using 0.01M, 0.05M or 0.1M HCl. 1.4 1 (27 bed volumes) ofcoloured water (initial true colour 57 Hazen units) was pumped througheach column at 4.4 m/h. Colour was eluted from the beds using 2 bedvolumes of 0.025M or 0.05M NaOH, followed by an acid rinse with 2 bedvolumes of HCl (same concentration as for the prewash).

Fractions of column effluent collected during treatment of colouredwater were analysed for true colour and during regeneration of the beds,were analysed for apparent colour. Colour removal after tworegenerations i shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________    Effect of Regenerant Concentration on Colour Removal by Packed Beds           Concentration                                                                         Concentration                                                                         Number of Bed Volumes with 100% true Colour Removal           NaOH (M)                                                                              HCl (M) 1st Run                                                                            After 1st Regeneration                                                                   After 2nd Regeneration                        __________________________________________________________________________    0.025   0.01    23    1          1                                            0.025   0.05    23   11         10                                            0.05    0.05    16   16         13                                            0.05    0.1     16   16         10                                            __________________________________________________________________________

EXAMPLE 11 Re-use of Chitin and Regenerants MultipleLoading/Regeneration Cycles of a Packed Bed

A 0.3 m column was packed with 14 g of hot 0.3M NaOH pretreated crabchitin, particle size 0.5 to 2.0 mm. The bed was prewashed with 2 l oftap water and 4 bed volumes of 0.05M HCl then loaded with 1.4 l (26 bedvolumes) of coloured water (57 Hazen units). Complete (100%) removal oftrue colour was achieved for 12 bed volumes.

The column was then regenerated using 2 bed volumes of 0.05M NaOHfollowed by 2 bed volumes of 0.1M HCl. Fractions of the effluent weremonitored for pH and apparent colour then pooled accordingly.Regenerants were made up to their original volume using 0.05M NaOH and0.1 M HCl and kept for use in the next regeneration cycle. Theloading/regeneration process was then repeated. In total one bed volumeof highly coloured but neutral solution was discarded and replaced withan equivalent volume of fresh acid or alkali after each regeneration.

The column was loaded with colour a total of nine times and regenerateda total of eight times. After the fifth regeneration the pH of thepooled NaOH fractions had fallen from the original pH 12.13 to pH 10.47and the pH of the pooled HCl fractions had increased from pH 1.41 to pH1.60. Subsequently the alkali regenerant was made up to the originalvolume and pH using 0.05M NaOH plus a small quantity of 1M NaOH and theacid regenerant was made up to the original volume and pH using 0.1M HClplus a small quantity of 1M HCl.

Following the first 4 regenerations, 11 bed volumes of water weretreated at 100% colour removal before breakthrough occurred. Six bedvolumes were treated at 100% colour removal following the last 4regenerations. However even after the passage of 26 bed volumes,removals in excess of 90% were obtained after 8 regenerations. Althoughthese colour removal performance results are not as high as in previoustests, they indicate that the chitin is maintaining its colour removalcapacity for at least 8 regeneration cycles. The pH and colour elutionprofiles demonstrated that colour was eluted in approximately one bedvolume and that the regenerants were effective at shifting pHreproducibly to release colour and then to recharge the chitin.

EXAMPLE 12 Performance of Crab Chitin Packed Bed

Four 1 m columns of particle size 0.5-2 mm, 0.3M NaOH pretreated crabchitin were linked in series and washed with water and four bed volumesof 0.01M HCl. 190 l (91 total bed volumes) of coloured water (30-32hazen units) were passed through the bed and 100% removal of true colourwas achieved by the first column alone.

The final three columns were regenerated using 4 bed volumes of 0.025MNaOH and 4 bed volumes of 0.01M HCl. A new column was packed and washedwith water and HCl and installed as the first column of the series. Aprefilter was placed in front of the four chitin columns to trapparticles, which consisted of a 1 m column packed with reticulated foampads. The prefilter column was backwashed daily. Approximately 365 l(183 total bed volumes) of coloured water (initial true colour 33 Hazenunits) were treated at 100% true colour removal.

After 200 l of water were treated the flow rate in this experiment fellgradually from 5.4 m/h to 2.8 m/h. The prefilter column was particularlysuccessful at trapping particulates, although flow rates still decreasedbetween the daily backwash treatments.

                  TABLE 6                                                         ______________________________________                                        Performance of a Packed Bed (4 × 1 m Beds Connected)                    of Crab Chitin at Colour Removal from Moorland Water                          ______________________________________                                        Number of bed volumes 183                                                     treated at 100% colour removal                                                Linear approach velocity                                                                            2.8-5.4                                                 (m.sup.3 /m.sup.2 /h)                                                         Bed Volume (liters)   2                                                       HCl Pretreatment (M)  0.01                                                    ______________________________________                                    

We claim:
 1. A method of decolourising water coloured by humic or fulvicacid without the use of a coagulant, which method comprises bringing thewater into contact with chitin or alginic acid as adsorbent.
 2. A methodaccording to claim 1 wherein the chitin is shellfish chitin.
 3. A methodaccording to claim 1 wherein the chitin is crab chitin.
 4. A methodaccording to claim 1 in which the water is moorland runoff water.
 5. Amethod according to claim 1 in which the water further contains metalions or particulate material which are adsorbed or trapped by theadsorbent.
 6. A method according to claim 1 which comprises continuouslypassing the water through a packed bed of absorbent.
 7. A methodaccording to claim 1 wherein the chitin is prewashed with an aqueousacid solution.
 8. A method according to claim 7 wherein the solution ishydrochloric acid at a concentration of from 0.01 to 0.05M.
 9. A methodaccording to claim 1 which further comprises recycling the adsorbent bycontact with an aqueous alkaline solution followed by contact with anaqueous acid solution.
 10. A method according to claim 9 in which theaqueous alkaline solution is a NaOH solution at a concentration of from0.01 to 0.1M.